Electron microscope including apparatus for x-ray analysis and method of analyzing specimens using same

ABSTRACT

There are provided an electron microscope including an apparatus of x-ray analysis, capable of performing elemental analysis with X-rays emitted from a specimen by electron beam irradiation, that is, inspection of foreign particles, for enhancement of yields in manufacturing semiconductor devices and so forth, at high speed and with high precision and high space resolving power, and a method of analyzing specimens using the same. The electron microscope comprises means of automatically controlling current quantity of the electron beam such that an X-ray count rate falls within a range of 1000 to 2000 counts per second, means of setting up a plurality of X-ray energy regions when checking an X-ray spectrum against reference spectra stored in a database for analysis of the X-ray spectrum, and performing matching for each of the X-ray energy regions, and means of analyzing distribution of elements observed on the basis of an intensity ratio between X-ray sample spectra obtained by electron beam irradiation at not less than two varied acceleration voltages, respectively.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an instrument system includingan electron microscope, for use as means for observation, analysis, andevaluation in research/development and manufacture of electronic devicesand micro-devices such as a semiconductor device, liquid crystal device,and magnetic head.

[0003] 2. Description of the Related Art

[0004] In the case of manufacturing devices like a memory, there arecases where foreign particles generated in the course of a manufacturingprocess are mixed therein. Examples of the foreign particles includeforeign species particles attributable to process material asrepresented by residue of etching, and residue of resist, wall materialof process vessels, material for fixedly holding a wafer, and materialfor vacuum gas line etc. Adhesion of the foreign particles to a waferresults in generation of defective items at times.

[0005] It is important from the viewpoint of improving a yield ofmanufacturing devices to analyze respective elemental composition of theforeign particles adhered to a wafer, and to search for generationsources of the foreign particles on the basis of their kinds, therebyremoving the causes of generation thereof.

[0006] As means for obtaining information on the elemental compositionsof specimens, there has been known a technique of irradiating anelectron beam, thereby detecting X-rays as generated. The X-rayscomprise a characteristic X-ray emitted when electrons of atoms on thesurface of, and in the vicinity of the surface of specimens falls froman excited state into a lower energy state, and a continuous X-ray at anenergy level below the energy of an incident electron beam due tobraking radiation whereby incident electrons are braked before emission.The characteristic X-ray has energy inherent to respective elements,indicated by K, L, and M lines, respectively, depending on the excitedstate of the characteristic X-ray. Accordingly, the elementalcomposition of specimens can be found by analyzing energy at peaksappearing in a spectrum. This method is called an energy dispersiveX-ray spectroscopy (EDX or EDS). Instruments for this method, suppliedby companies such as Oxford Instrument, EDAX, TermoNORAN Instrument, andso forth, are available in the market, and are capable of making bothqualitative analysis and quantitative analysis. Users can find theelemental composition of specimens by analyzing obtained spectra bymeans of qualitative analysis and quantitative analysis, respectively.

[0007] Another example of a method of identifying the elementalcomposition of specimens from X-ray spectra is disclosed in JP-A No.108253/1988 (public known example 1). There is described therein themethod whereby respective characteristic X-ray spectra (referencespectra) of a plurality of known substances are kept registered in amemory, and by checking the X-ray spectrum of an unknown substanceagainst the reference spectra registered in the memory, the unknownsubstance is identified.

[0008] An example of inspecting foreign particles on the surface of awafer by use of the method described is disclosed in JP-A No. 14811/1996(public known example 2). In this example, there is described aconfiguration wherein the locations of foreign particles are determinedby observation of images dependent on the magnitude of reflectionelectron signals, and by checking the X-ray spectra of the foreignparticles against reference spectra, the elemental compositions of theforeign particles can be identified.

[0009] Still another method is disclosed in JP-A No. 321225/2000 (publicknown example 3). There is described therein a method wherein the netX-ray spectrum of a foreign particle is found on the basis of an X-rayspectrum of a portion of the surface of a wafer, having the foreignparticle, and an X-ray spectrum of the rest of the surface of the wafer,having no foreign particle, (background spectrum), and the elementalcomposition of the foreign particle is found by checking the net X-rayspectrum of the foreign particle against a database.

[0010] Further, there is disclosed in JP-A No. 68518/2001 a method ofgeneralizing information on foreign particles, found by the methoddescribed above, and registering the same into predetermined categories,thereby specifying causes of defects.

[0011] An electron beam, even if focused in a narrow region, issubjected to interaction with substance inside a specimen upon fallingon the specimen, thereby undergoing scattering. The magnitude of ascattering region is dependent on an element as the constituent of thespecimen and an acceleration voltage of the electron beam. FIGS. 18Athrough 18D are views of results of calculation by a Monte Carlo method,showing electron beam scattering conditions when electron beams withacceleration voltage at 15 kV, and 5 kV, respectively, are irradiated tospecimens of silicon (Si) and tungsten (W), respectively. In the case ofthe specimen being silicon, the magnitude of a scattering region of theelectron beam is about 4 μm if the acceleration voltage is 15 kV, andabout 0.4 μm if the acceleration voltage is 5 kV. Due to excitation ofthe electron beams, X-rays are generated substantially in these regions,respectively. This means that X-ray spectra as observed reflectinformation on not only irradiation points of the electron beams butalso substances contained in the respective scattering regions.Accordingly, space resolving power in elemental analysis is determinednot by the size of an electron beam but by the magnitude of thescattering region.

[0012] Since processing sizes of semiconductor elements that haveattained miniaturization have lately reached sub-micron levels, sizes offoreign particles causing degradation in the characteristics of theelements have also become smaller. FIG. 19 is a view showing asemiconductor device structure during a manufacturing process, beingmatched against the respective scattering regions of the electron beams,inside Si, as shown in FIGS. 18A and 18B. In the case of EDX analysis ofa small foreign particle, an electron beam passes through the foreignparticle, and scatters inside a substrate. Accordingly, an X-rayspectrum as observed contains information on both the foreign particle,and the substrate (background), causing difficulty with analyzing. Witha substrate in the middle of a manufacturing process, in particular,patterns, that is, an oxide film, electrodes, a dielectric film, and soforth, are formed on the substrate, and in case that flakes from thosesubstances constitute foreign particles, the foreign particles need tobe distinguished from those substances.

[0013] Further, if the acceleration voltage is lowered in order toreduce the effect of the background, that is, to reduce the size of thescattering region, characteristic X-rays that can be excited arerestricted, in which case, elements need to be identified withoverlapping characteristic X-ray peaks. Such an instance is describedwith reference to FIG. 20. FIG. 20 is a profile showing X-ray spectra ofa titanium (Ti) foreign particle 50 nm thick, present on the surface ofa silicon wafer. The X-ray spectra were obtained by two electron beamsat 15 kV, and 5 kV, of the acceleration voltage, respectively. In thecase of the acceleration voltage at 15 kV, a Ti-K line peak is observedat 4.51 keV of X-ray energy, however, in the case of the accelerationvoltage at 5 kV, such a peak is not observed because such acharacteristic X-ray cannot be excited. In this case, presence oftitanium element is determined by a Ti-L line observed at 0.45 keV ofX-ray energy. However, since there exist K-line peaks of oxygen andnitrogen, respectively, in this region of X-ray energy, characteristicX-ray peaks are observed in overlapped state, if those elements arepresent, causing difficulty with analyzing.

[0014] Further, in the case of lowering the acceleration voltage, agenerated quantity of X-ray decreases although current is sufficient forobservation of secondary electron images. For example, in theabove-described instance, if setting of the acceleration voltage only ischanged from 15 kV to 5 kV, the generation quantity of the X-ray havingthe Ti-L line peak is one tenth of the generation quantity of the X-rayhaving the Ti-K line peak, at the acceleration voltage of 15 kV, mainlyused for identification of Ti element, thereby causing a problem ofdegradation of accuracy in identification of elements.

[0015] Furthermore, the following problems have been encountered withthe conventional methods described in the foregoing.

[0016] Analysis by software for qualitative analysis and quantitativeanalysis, attached to X-ray detectors available in the market, relies ona manual, which is too complicated to be used by a lay user, and isinsufficient for controlling process steps, so that there has been ademand for a system automatically outputting elemental composition.

[0017] The methods according to the public known examples 1 and 2,respectively, are effective against specimens of a uniform elementalcomposition, however, in the case of a small foreign particle on asubstrate, there has been a problem in that even with foreign particlesof an identical elemental composition, X-ray spectra thereof largelydiffer from each other depending on a size (thickness) of the foreignparticles as shown FIGS. 21A and 21B, resulting in failure to match withthe reference spectra stored in the database. Although it is conceivableto prepare X-ray spectra corresponding to varied thickness of foreignparticles, this has caused a problem of requiring longer checking timebecause of an increase in the number of the reference spectra. Further,since sensitivity (spectral sensitivity) against X-ray energy generallyvaries on a case-by-case basis due to variations in performance of X-raydetectors, and difference between optical systems for detection, thereis a need for preparing X-ray spectra to be prepared as a database forevery instrument. Furthermore, spectral sensitivity undergoes a changeover time due to stains etc. on an X-ray window, causing at times aproblem with checking of an X-ray spectrum.

[0018] The method according to the public known example 3 is a methodwherein the net X-ray spectrum of a foreign particle is found on thebasis of the X-ray spectrum of the portion of the surface of the wafer,having the foreign particle, and the X-ray spectrum of the rest of thesurface of the wafer, having no foreign particle, (the backgroundspectrum), and the elemental composition of the foreign particle isfound by checking the net X-ray spectrum of the foreign particle againstthe data base. In this case, there has been encountered a problem of apossibility that erroneous results are obtained because components ofthe X-ray spectrum from the background varies depending on the size ofthe foreign particle, that is, this is not a case of a simple linear sumof the background spectrum and the X-ray spectrum of the foreignparticle portion. The problem will be described by way of example withreference to FIG. 22. A figure in the left part of FIG. 22 is aschematic representation showing a case where an electron beam 8 isirradiated to a silicon wafer 20 incorporating body structures 70 madeof an element A. The electron beam 8 scatters in a region 71hemispherical in shape inside the silicon wafer 20, and in the casewhere the body structures 70 are present within the region 71, an X-rayspectrum as observed comprises the characteristic X-ray peak of siliconand that of the element A. Meanwhile, a figure in the right part of FIG.22 is a schematic representation showing a case where a foreign particle22 made of the element A is present on the surface of the same siliconwafer. A scattering region of an electron beam 8 will be a region 71smaller than the region shown in the left figure due to the presence ofthe foreign particle 22. An X-ray spectrum as observed in this case aswell has the characteristic X-ray peak of silicon and that of theelement A. There are cases where the X-ray spectrum obtained in the caseof the right figure becomes substantially the same as that in the caseof the left figure, in which case there has occurred a problem in thatthe peaks will disappear upon subtracting the X-ray spectrum obtained inthe case of the right figure from the X-ray spectrum obtained in thecase of the left figure, representing the background.

SUMMARY OF THE INVENTION

[0019] In view of the problems described above, it is an object of theinvention to provide an electron microscope including an apparatus ofx-ray analysis, capable of analyzing the elemental composition offoreign particles on the surface of a specimen with high space resolvingpower, high precision, and high throughput, and a method of analyzingspecimens using the same.

[0020] The object of the invention can be achieved by adoption of thefollowing configuration:

[0021] (1) An electron microscope according to the invention ischaracterized in that the current quantity of an electron beam iscontrolled such that the count-number of X rays from the specimens fallswithin a range of 1000 to 2000 counts per second.

[0022] The electron microscope having an electron beam optical systemprovided with an electron source and a lens for focusing an electronbeam, an optical system controller for controlling the electron beamoptical system, a specimen stage on which specimens are to be placed, anelectron detector for detecting electrons emitted from the specimens byirradiating the specimens with the electron beam, an X-ray detector fordetecting X rays radiated from the specimens, and a processor forprocessing signals from both the detectors, and performing imageformation and elemental analysis of the specimens, comprises means ofdetecting the count-number of X rays per unit time by detecting the Xrays with the X-ray detector, and feedback-controlling the currentquantity of the electron beam on the basis of the count-number of X raysper unit time. Further, the current quantity of the electron beam isfeedback-controlled such that the count-number of X rays from thespecimens falls within the range of 1000 to 2000 counts per second.

[0023] As a result, the invention can provide the electron microscopecapable of securing a large generation quantity of X rays without theneed for a user manually adjusting beam current, and without a risk ofimpairing performance of the X-ray detector.

[0024] (2) The electron microscope according to the invention mayfurther comprise a database having data including X-ray spectra(reference spectra) of a plurality of kinds of standard substances andlabels containing names of substances corresponding to the respectivereference spectra, and means comprising steps of:

[0025] checking an X-ray spectrum (sample spectrum) of the specimensagainst the reference spectra in the database;

[0026] calculating degree of matching in spectral shape between thesample spectrum and the reference spectra;

[0027] extracting a reference spectrum having the highest degree ofmatching from the database;

[0028] setting up a plurality of X-ray energy regions so as to havesensitivity data for X-ray energy of the X-ray detector, and to includepeaks of the sample spectrum when analyzing by identifying substances ofthe specimens on the basis of the label corresponding to the referencespectrum extracted;

[0029] standardizing intensity of the reference spectra into intensityof the sample spectrum for each of the X-ray energy regions as set upafter multiplying the reference spectra by the sensitivity data;

[0030] checking the sample spectrum against the reference spectra asstandardized and extracting one or a plurality of the reference spectrain descending order of the degree of matching between the samplespectrum and the reference spectra for each of the X-ray energy regions;and

[0031] outputting the label or labels corresponding to the one or theplurality of the reference spectra, the degree of matching, and anumerical value used in the standardization.

[0032] Further, a function of outputting the label, the degree ofmatching, and the numerical value as described above may output, forexample, first to third candidate elements in descending order of thedegree of matching. Still further, the electron microscope according tothe invention may display a intensity ratio of the sample spectraobtained by electron beam irradiation at not less than two variedacceleration voltages is displayed. Furthermore, the sensitivity datamay contain an intensity ratio of an X-ray spectrum of a standardspecimen including a silicon wafer, obtained at the time of obtainingthe reference spectra to an X-ray spectrum of the standard specimen,obtained immediately before matching.

[0033] Accordingly, it becomes possible to implement analysis ofelements which spectra are overlapped with each other, and to obtaininformation on which element is contained in a foreign particle bychecking the X-ray spectrum of the foreign particle as well as asubstrate under the foreign particle, in a region different in size, sothat the electron microscope capable of analyzing elements andsubstances with high sensitivity and high precision can be provided.Further, since difference in spectral sensitivity, between instruments,can be corrected by a correction curve using a standard specimen, itneed only be sufficient to prepare one kind of database, which can bereinforced with a database acquired in another instrument withoutwasting the latter. Still further, even if the spectral sensitivity ofthe same instrument undergoes a change due to stains, etc. on the X-raywindow, it is possible to effectively maintain matching with a databaseby acquiring a correction curve by use of a standard specimen.

[0034] (3) The electron microscope according to the invention mayfurther comprise a memory for storing a plurality of X-ray spectra(sample spectra) at a plurality of observation points on the specimens,respectively, obtained by the X-ray detector, and means of categorizingthe plurality of the sample spectra into one or a plurality of groups ofthe sample spectra by matching thereof with each other, and performingelemental analysis of one X-ray spectrum selected from the respectivegroups.

[0035] Furthermore, the electron microscope according to the inventionmay comprise a function of matching the sample spectra with each otherfor each of one or a plurality of X-ray energy regions set up so as toinclude respective peaks of the sample spectra.

[0036] Further, the electron microscope according to the invention mayautomatically categorize the plurality of the sample spectra by matchingthereof with each other, and perform elemental analysis of the pluralityof the sample spectra as categorized.

[0037] Thus, it becomes possible to categorize on the basis ofrepresentative spectra without checking an X-ray spectrum obtained atevery foreign particle point against a database every time the X-rayspectrum is obtained, so that the invention can provide the electronmicroscope capable of analyzing elemental composition of respectiveforeign particles in short time by matching the representative spectraonly against the database, or performing qualitative analysis orquantitative analysis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a schematic side view of a first embodiment of aninstrument according to invention, showing the configuration of theinstrument in its entirety;

[0039]FIG. 2 is a schematic plan view of the first embodiment of theinstrument according to invention, showing the configuration of theinstrument in its entirety;

[0040]FIG. 3 is a partly sectional perspective view of the instrumentaccording to the first embodiment of invention;

[0041]FIG. 4 is a flow chart showing a method of automatically settingelectron beam irradiation condition according to the first embodiment ofinvention;

[0042]FIG. 5 is a profile showing an example of an X-ray spectrumobtained according to the first embodiment of invention;

[0043]FIG. 6 is a flow chart showing a method of matching X-ray spectraaccording to a second embodiment of invention;

[0044]FIG. 7 is a view showing a display example of output results ofelemental analysis, according to the second embodiment of invention;

[0045]FIG. 8 is a view showing another display example of output resultsof elemental analysis, according to the second embodiment of invention;

[0046]FIG. 9 is a flow chart showing a method of performing elementalanalysis according to a third embodiment of invention;

[0047]FIG. 10 is a flow chart showing a method of performing elementalanalysis according to a fourth embodiment of invention;

[0048]FIG. 11 is a profile showing an example of an X-ray spectrumobtained according to the fourth embodiment of invention;

[0049]FIGS. 12A and 12B are views showing the principle of operationaccording to the fourth embodiment of invention;

[0050]FIG. 13 is a graph showing an example of an intensity ratiobetween X-ray spectra according to the fourth embodiment of invention;

[0051]FIG. 14 is a graph showing an example of an intensity ratiobetween reference spectra according to the fourth embodiment ofinvention;

[0052]FIG. 15 is a graph showing an example of a ratio of spectralsensitivity for use in matching of spectra according to the embodimentsof invention;

[0053]FIGS. 16A through 16C are schematic representations forillustrating the principle on which a variation of the fourth embodimentis based;

[0054]FIGS. 17A through 17C are schematic diagrams of X-ray spectraaccording to the variation of the fourth embodiment.

[0055]FIGS. 18A through 18D are schematic sectional views showingdependency of electron beam scattering inside specimens, on atomicnumbers and acceleration voltages;

[0056]FIG. 19 is a view showing relationship in position betweenelectron beam scattering regions inside a specimen and a typicalsemiconductor;

[0057]FIG. 20 is a profile showing comparison of X-ray spectra obtainedat varied acceleration voltages;

[0058]FIGS. 21A and 21B are views showing dependency of X-ray spectra offoreign particles adhered to the surface of a wafer on thickness of theforeign particles; and

[0059]FIG. 22 is a schematic sectional view of a specimen forillustrating difference between an X-ray spectrum of a portion of thespecimen, having no foreign particle, and an X-ray spectrum of a portionof the specimen, having a foreign particle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Embodiments of an electron microscope including an apparatus ofx-ray analysis, and a method of analyzing specimens using the same,according to the invention, are described hereinafter in respect ofconfiguration and operation thereof.

[0061] First Embodiment

[0062] Instrument configuration and operation according to a firstembodiment of the invention are described hereinafter with reference toFIGS. 1 through 5. FIGS. 1 and 2 show the configuration of an instrumentin its entirety, and FIG. 3 shows in detail the configuration of ascanning electron microscope optical system and the periphery of aspecimen stage. With the present embodiment, there is shown a portion ofthe electron microscope according to the invention, applicable to awafer. Further, FIG. 3 is a partly sectional perspective view of theinstrument shown in FIG. 1 although there exists some differencetherebetween in respect of the orientation of the instrument and indetail for the sake of convenience in description, however, there is, ineffect, no difference.

[0063] In FIG. 1, an electron beam optical system 1 and an X-raydetector 16 are suitably disposed in an upper part of a vacuum specimenchamber 60 at the central part of an instrument system. A specimen stage24 on which a wafer 20 as a specimen is to be placed is disposed insidethe vacuum specimen chamber 60. Two units of optical system 31, 41 areadjusted such that respective center axes thereof intersect each otherat one point in the vicinity of the surface of the wafer 20. Thespecimen stage 24 has a built-in mechanism moving the wafer 20 back andforth, and from side to side, with high precision, controlling such thata designated spot on the wafer 20 comes directly below the electron beamoptical system 1. Further, the specimen stage 24 has a function ofrotating, turning upside down, or tilting. The vacuum specimen chamber60 is connected to an exhaust system (not shown), and is controlled soas to be in a suitable vacuum. Further, the electron beam optical system1 as well is provided with an individual exhaust system (not shown)thereby maintaining a suitable degree of vacuum. Wafer introductionmeans 61 and wafer carrying means 62 are provided inside the vacuumspecimen chamber 60. A wafer transfer robot 82 and cassette introductionmeans 81 are disposed so as to be adjacent to the vacuum specimenchamber 60. There are disposed a main controller 100 for controlling andmanaging a series of processes for the instrument in whole, and an X-raydetector controller 101, on the left side of the vacuum specimen chamber60 so as to be adjacent thereto. The main controller 100 and the X-raydetector controller 101 are set up such that data can be mutuallyexchanged therebetween, and the main controller 100 can control theX-ray detector controller 101.

[0064] Now, an operation of wafer introduction, according to the presentembodiment, is broadly described hereinafter. When a wafer cassette 23is placed on a table of the cassette introduction means 81, and acommand for starting the operation is issued from the main controller100, the wafer transfer robot 82 takes out a wafer 20 as a specimen froma designated slot inside the wafer cassette 23, and orientationadjustment means 83 shown in FIG. 2 adjust orientation of the wafer 20toward a predetermined position. Subsequently, at a point in time when ahatch 64 in the upper part of the wafer introduction means 61 is openedby the wafer transfer robot 82, the wafer 20 is placed on a stage 63.Upon closing the hatch 64, air is exhausted by vacuum exhaust means (notshown), and thereafter, the wafer carrying means 62 picks up the wafer20 on the stage 63, placing the same on the specimen stage 24 inside thevacuum specimen chamber 60. In this connection, the specimen stage 24 isprovided, as necessary, with means for chucking the wafer 20 to correctwarpage thereof or to prevent vibration thereof.

[0065] Next, referring to FIG. 3, the electron beam optical system andX-ray detector are described. With the electron microscope according tothe invention, the electron beam optical system 1 comprises an electrongun 7, an electron lens 9 for focusing the electron beam 8 released fromthe electron gun 7, an aperture 3 for cutting unnecessary portions ofthe electron beam 8, a blanking coil 4, a Faraday cup 5, an electronbeam scanning coil 10, and an objective lens 11. The Faraday cup 5 has athrough-hole for allowing the electron beam 8 to pass therethrough, andthe blanking coil 4 deflects the electron beam 8 from the through-holeof the Faraday cup 5 only when measuring current of the electron beam 8before causing the electron beam 8 to fall on the Faraday cup 5. Besidesthe above-described components, there are provided a secondary electrondetector 6 for detecting secondary electrons from the wafer 20, emittedupon irradiation of the electron beam 8 onto the wafer 20, the specimenstage 24 which is movable and on which the wafer 20 is placed, the X-raydetector 16 for detecting X rays radiated from the wafer 20 a at thetime of the irradiation of the electron beam 8 onto the wafer 20, and areflection electron detector (not shown) for detecting reflectionelectrons emitted from a specimen. The electron beam optical system,specimen stage, secondary electron detector, and reflection electrondetector are controlled by the main controller 100.

[0066] Now, with the present embodiment, there is broadly describedhereinafter a process of evaluation mainly on elemental compositionafter introduction of the wafer 20.

[0067] Upon the electron beam 8 falling on the wafer 20, secondaryelectrons and reflection electrons, reflecting the surface geometry ofthe wafer 20, are emitted from the surface of the wafer 20, and at thesame time, there are produced X-rays containing characteristic X-rayshaving energy inherent to elemental composition of portions of the wafer20, in the vicinity of electron beam incident regions. By moving thespecimen stage 24 such that a desired observation region on the wafer 20comes directly below the electron beam optical system 1, the electronbeam 8 is caused to scan the surface of the observation region with adeflection lens, and foreign particles on the wafer 20 are observed onthe basis of secondary electron images and reflection electron images,obtained by detecting the secondary electrons and reflection electronsemitted from the wafer 20, adjustment being made such that the foreignparticles are positioned at the center of the observation region.Subsequently, X rays produced by irradiation of the foreign particleswith the electron beam 8 kept in stationary state are detected by theX-ray detector 16, thereby obtaining an X-ray spectrum. Thereafter, byanalyzing the X-ray spectrum, elemental composition of the foreignparticles is found. The X-ray spectrum and results of analysis are shownon a display inside the main controller 100, and are stored in a memoryat the same time. On the basis of the coordinates of a position of eachof the foreign particles on the wafer 20, obtained by an optical foreignparticle inspection apparatus, the specimen stage can be controlled suchthat the foreign particles enter the observation region.

[0068] As shown in FIGS. 18 and 19, acceleration voltage of the electronbeam 8 is characterized in that the lower the acceleration voltage is,the smaller the scattering region of the electron beam 8, inside thewafer 20, becomes. When observing the foreign particles on the wafer 20,electrons penetrating through the foreign particles scatter inside thewafer 20, so that a substance, existing in the vicinity of regionsunderneath the foreign particles, is mixed as a background noise intothe X-ray spectrum as observed. From the viewpoint described as above,it can be said that the lower the acceleration voltage is, the moreconvenient it is from a point of elemental analysis of the foreignparticles. This is effective particularly when body structures composedof several elements are formed in the vicinity of the surface of thewafer 20. On the other hand, if the acceleration voltage is lowered, thecharacteristic X-rays that can be excited are restricted, so that theelements that can be analyzed are also restricted. Accordingly, in thecase where semiconductor elements submicron in size are being formed,the acceleration voltage at several kilovolts (kV) is adopted.

[0069] A high count-number of an X-ray spectrum with high-energyresolving power is necessary for elemental analysis with high precision.With the X-ray detector according to the present embodiment, use is madeof a cooled silicon semiconductor detection element, and in order totake measurements without impairing energy resolving power andefficiently, that is, with minimum omission in counting, it ispreferable to cause X rays ranging from 1000 to 2000 in number to fallon the specimen per second. The count-number of X rays per second iscalled an X-ray count rate, and cps (counts per second) is generallyused as units thereof. With the present embodiment of the invention, theX-ray count rate can be measured with the X-ray detector controller.

[0070] In the case where electron beams of an identical current strengthare irradiated onto a silicon wafer with acceleration voltage at 15 kV,and 5 kV, respectively, the X-ray count rate in the case of 15 kV isabout ten times as large as that in the case of 5 kV. Accordingly, inorder to perform observation with a high X-ray count rate, there is aneed for adjusting current quantity so as to correspond to anacceleration voltage.

[0071]FIG. 4 is a flow chart showing setting of an operation conditionof the electron beam optical system. With the present embodiment of theinvention, as shown in FIG. 4, after setting an acceleration voltage atfirst, an initial value of current strength is set to, for example, 100pA, the wafer 20 is irradiated, and the main controller 100 receives anX-ray count rate from the X-ray detector controller 101. The maincontroller 100 increases or decreases current strength of the electronbeam 8 so as to correspond to the X-ray count rate. As a result of sucha step of operation as described, the X-ray count rate is set to anoptimum value for detection of X rays, in a range of 1000 to 2000 cps.However, since a maximum value of electron beam current is dependent onan instrument in use, the beam current is set to the maximum value ofthe instrument in case a set value as above comes to exceed the maximumvalue.

[0072]FIG. 5 is a profile showing an X-ray spectrum of a foreignparticle of titanium (Ti), 50 nm thick, present on the surface of asilicon wafer, obtained as a result of setting the operation conditionof the electron beam optical system, as described above. The height(count-number from a background X-ray signal level) of a Ti-L line peakappearing at 0.45 keV of X-ray energy becomes about 150 counts, higherby about one order of magnitude during equivalent measuring time, ascompared with the X-ray spectrum of the foreign particle of titanium(Ti), obtained with the acceleration voltage with at 5 kV, as shown inFIG. 20, thereby obtaining a peak height sufficient for analysis, sothat elemental analysis with a high S/N ratio can be attained. Hence,observation with high resolving power and high precision becomespossible.

[0073] Second Embodiment

[0074] A second embodiment of an electron microscope including anapparatus of x-ray analysis, and a method of analyzing specimens usingthe same, according to the invention, is described hereinafter withreference to FIG. 3 and FIGS. 6 through 8. FIG. 6 is a flow chartshowing a method of analyzing X-ray spectra. FIGS. 7 and 8 are viewsshowing an X-ray spectrum and output results of analysis, shown on adisplay of a main controller, respectively.

[0075] An X-ray detector controller 101 according to the presentembodiment, which is the same in configuration as that shown in FIG. 3,has a qualitative analysis function of presuming a candidate element onthe basis of an X-ray energy value corresponding to a peak of an X-rayspectrum, and other functions as described hereinafter. Further, theX-ray detector controller 101 has a memory, and a database containing aplurality of X-ray spectra (reference spectra), against which an X-rayspectrum as obtained is checked, is stored in the memory. Individualreference spectra are designated by specimen names correspondingthereto, respectively. The reference spectra are prepared for substancesused in manufacturing semiconductor elements, such as silicon, oxygen,copper, tungsten, gold, titanium, tantalum, titanium nitride TiN,tantalum nitride TaN, silicondioxide SiO2, and so forth. Furthermore, amain controller 100 is capable of exchanging information with the X-raydetector controller 101, and has functions of controlling the X-raydetector controller 101, receiving necessary information from the X-raydetector controller 101 to thereby show the information on a display ofthe main controller 100, and storing the information in the memory.

[0076] In accordance with the flow chart shown in FIG. 6, the method ofanalyzing the specimens is described hereinafter. First, qualitativeanalysis is performed on an X-ray spectrum of a foreign particle,obtained as described in the first embodiment, and the X-ray spectrumand results of the qualitative analysis are shown on the display asshown in FIG. 7. In FIG. 7, element names displayed above respectivepeaks of the X-ray spectrum represent the results of the qualitativeanalysis. Next, a region for use in checking the X-ray spectrum againstthe database is set up. The region for use in checking is referred to anROI (region of interest). With the present embodiment, a plurality ofthe ROIs are set up so as to include a portion of the base,corresponding to the respective peaks of the X-ray spectrum, as shown inFIG. 7. The ROIs are set up by a method of deeming portions of the X-rayspectrum, on the upper side of the background, that is, on the plus sidethereof, as the ROIs. After setting up the ROIs, the ROIs and numberscorresponding thereto are displayed by double-headed arrows,respectively (highlighting of the ROIs). In the case where peaks of theX-ray spectrum are overlapped with each other, as with the case of anROI indicated by #1 in FIG. 7, this is deemed as one ROI. Subsequently,for each of the ROIs that are set up, the X-ray spectrum is checkedagainst X-ray spectra in the database stored in the memory of the X-raydetector controller 101 (matching). FIG. 8 shows results of matching,displaying three lists in descending order of matching scope and degreeof matching for each of the ROIs. The degree of matching is evaluated byX2 represented by the following expression: $\begin{matrix}{x^{2} = {\sum\limits_{i = {m1}}^{m2}{\left( {{aT}_{i} - L_{i}} \right)^{2}/L_{i}}}} & {{expression}\quad (1)}\end{matrix}$

[0077] where Ti, Li represent the value of the X-ray spectrum to bechecked, and respective values of the X-ray spectra in the database,respectively, m1, m2 are energy at a start point and an end point, ofthe respective ROIs, respectively, and a is parameter for use inaligning the height of a peak in the respective ROIs with that of thereference spectra to be checked against. In case there exist a pluralityof peaks within each of the ROIs, the highest peak is used for matching.On the presumption that the smaller the value of X², the better thedegree of matching is, there are displayed results showing X², a,respective labels of the reference spectra in descending order of degreeof matching. With the present embodiment, matching is performed for thefull range of acquired energy besides the ROIs as set up, outputtingresults of such matching as shown in the bottom row of a table in FIG.8. This is effective for analysis of very thick foreign particles.

[0078] In FIG. 8, columns denoted by best, second, and third,respectively, indicate descending order of the degree of matching. TheX-ray spectrum obtained is shown to have best matched with the referencespectrum with a label designated as TiN (titanium nitride). In thecolumn of energy regions, start values and end values are shown in unitsof keV, respectively. It becomes possible to obtain informationconcerning an element or thickness of a substance, corresponding to theparameter a, on the basis of the parameter a.

[0079] The main controller 100 stores information shown in the table inFIG. 8 together with secondary electron images, reflection electronimages, and position information, in the memory, and displays elementaldistribution of the foreign particle on a wafer on the basis of theposition information and the information shown in the table in FIG. 8.Furthermore, the main controller 100 provides a user with presumedresults concerning causes for generation of the foreign particle bychecking against a database showing relationship with processing steps.

[0080] As described in the foregoing, with the present embodiment, sincethe X-ray spectrum as obtained is checked against the X-ray referencespectra in the database for each of the ROIs, it becomes possible toavoid a problem that respective X-ray spectra of foreign particles cometo significantly differ from each other depending on the size(thickness) thereof even if the foreign particles are the same inelemental composition, resulting in failure to match with any of theX-ray reference spectra stored in the database. This will eliminate theneed for preparing X-ray reference spectra for foreign particles withvaried thickness, so that the number of X-ray reference spectra to bechecked against can be reduced, thereby enabling matching to be executedwith high throughput.

[0081] In the case where X-ray detection of a foreign particle oftungsten is performed by an electron beam with the acceleration voltageat 5 kV, the characteristic X-ray peak attributable to tungsten comes tobe overlapped with the characteristic X-ray peak attributable to siliconor tantalum (Ta), so that it is difficult to discriminate therebetweenby merely observing X-ray spectra thereof. However, with the use of thismethod, it has since become possible to discriminate therebetween withhigh precision. With the present embodiment, in executing matching foreach of the ROIs, there are displayed matching results of up to threecases in descending order of degree of matching, however, there may bedisplayed instead matching results of cases where X2 as an indicator ofthe degree of matching is not greater than a predetermined value.Further, the ROIs are set up automatically, however, a method of a usersetting up the ROIs by inputting the same may be used in combinationwith the foregoing method. Furthermore, X2 represented by the expression(1) is adopted as the indicator of the degree of matching, however, itis to be pointed out that the advantageous effects of the invention arenot impaired by use of another method of adopting the sum of the squareof remainder between both the X-ray spectra, and so forth, as anindicator of the degree of matching.

[0082] Third Embodiment

[0083] A third embodiment of the invention is described hereinafter withreference to FIG. 9. With the present embodiment, the configuration ofan instrument is the same as that described in the first and secondembodiments, respectively, but a method of analyzing specimens differsfrom that for the first embodiment and the second embodiments,respectively.

[0084] As shown in FIG. 9, with the present embodiment, firstly, X-rayspectra of a plurality of foreign particles to be evaluated are obtainedbeforehand, and are stored in a designated region of the memory providedin the X-ray detector controller 101 shown in FIG. 3 (a group of X-rayspectra of foreign particles). Respective X-ray spectra are providedwith labels corresponding to respective coordinates of positions of theforeign particles, and are stored so as to be able to identify which ofthe X-ray spectra corresponds to a foreign particle located at whichposition.

[0085] Subsequently, ROIs are set up for a specific X-ray spectrum ofthe group of the X-ray spectra of the foreign particles as with the caseof the second embodiment, and by checking the specific X-ray spectrumagainst other X-ray spectra of the group of the X-ray spectra of theforeign particles, the group of the X-ray spectra of the foreignparticles is categorized into subgroups of the X-ray spectra having ahigh degree of matching with each other. Next, one X-ray spectrum isselected from one of the subgroups of the X-ray spectra, as categorized,and is checked against the X-ray reference spectra in the database inaccordance with the procedure described in the second embodiment,thereby identifying an element and a substance on the basis of an X-rayreference spectrum matching the respective subgroups.

[0086] With the present embodiment, instead of checking the respectiveX-ray spectra of all the foreign particles for inspection against theX-ray reference spectra, the X-ray spectra of the foreign particles arecategorized into the subgroups of the X-ray spectra beforehand, and oneX-ray spectrum selected from the respective subgroups is checked againstthe X-ray reference spectra, thereby identifying an element and asubstance. Accordingly, operation on the whole can be implemented withhigh throughput. This method is effective particularly in the case whereforeign particles on a wafer, as the objects for inspection, aregenerated due to a certain cause, and are composed of substantially anidentical substance.

[0087] With the first through third embodiments as described above, ifthe spectral sensitivity of the X-ray detector varies when checking anX-ray spectrum obtained against the X-ray reference spectra in thedatabase, matching precision deteriorates. The spectral sensitivityundergoes variation due to variation with respect to an X-ray detectionelement of the X-ray detector controller and an X-ray transmissionwindow of the X-ray detector, mounting position of the X-ray detector,relative to the electron microscope (a distance from a specimen to theX-ray detection element, and an X-ray takeout angle), deterioration oftransmittance caused by contamination of the X-ray transmission windowafter mounting, and so forth. FIG. 15 shows a ratio of spectralsensitivity with reference to an X-ray spectrum from the same siliconspecimen, obtained by another electron microscope with a different X-raydetector mounted thereon.

[0088] With the embodiments of the invention, a ratio of spectralsensitivity in the database to spectral sensitivity at the time ofmeasurement, as shown in FIG. 15, is obtained beforehand, and matchingis performed with the ratio of spectral sensitivity described beingtaken into consideration in order to prevent deterioration in matchingprecision, due to variation in spectral sensitivity. In addition, sincethere can be a case of the spectral sensitivity undergoing a change dueto contamination of the X-ray transmission window, and replacement ofthe X-ray detector, it is preferable to periodically measure a new ratioof spectral sensitivity.

[0089] By so doing, the need for preparing a database for everyinstrument is eliminated, so that it becomes possible to make effectiveuse of the database.

[0090] Furthermore, by copying a file for X-ray spectra, the same can beadded to the database with ease.

[0091] Fourth Embodiment

[0092] A fourth embodiment of the invention is described hereinafterwith reference to FIG. 5 and FIGS. 10 through 14. With the presentembodiment, there is shown an example of a method of analyzing theelemental composition of a foreign particle with high precision byelectron beam irradiation at varied acceleration voltages.

[0093] With the present embodiment, as shown in a flow chart of FIG. 10,firstly, by electron beam irradiation with acceleration voltage at 5 kV,an X-ray spectrum of a foreign particle on a wafer is obtained and isdesignated as A to be stored in a memory provided in an X-ray detectorcontroller. Subsequently, by electron beam irradiation with accelerationvoltage at 3 kV, an X-ray spectrum of the same foreign particle isobtained and is designated as B to be similarly stored in a memory.

[0094] Thereafter, an intensity ratio of a spectrum B to a spectrum A(B/A) is calculated, and by comparing B/A with a database, there aredisplayed results of determination on which element corresponds to theelement of the foreign particle, and which element corresponds to theelement of a substrate.

[0095] A case example is described hereinafter. FIGS. 5 and 10 show anX-ray spectrum obtained by irradiating a foreign particle on a waferwith an electron beam with acceleration voltage at 5 kV, and 3 kV,respectively. With either of the X-ray spectra, three characteristicpeaks are observed, and are identified as carbon, titanium, and silicon,respectively, in ascending order of energy intensity. FIG. 13 shows anintensity ratio of the X-ray spectrum shown in FIG. 5 to that shown inFIG. 11. For reference, the X-ray spectrum corresponding to the electronbeam irradiated with acceleration voltage at 3 kV is shown by a graph inthe lower part in the figure. The vertical axis is adjusted for easyviewing, and the horizontal axis indicates X-ray energy intensity. FIG.14 shows an intensity ratio of an X-ray spectrum of a compound composedof uniformly distributed titanium and silicon against an electron beamirradiated with acceleration voltage at 5 kV to the same at 3 kV. TheX-ray spectrum shown in the lower part in the figure is onecorresponding to the electron beam irradiated with acceleration voltageat 3 kV. It can be seen by comparing FIG. 13 with FIG. 14 that atitanium peak at 0.45 keV of X-ray energy differs in trend from asilicon peak at 1.75 keV of X-ray energy. More specifically, in a part(background X-ray) of FIG. 13 as well as FIG. 14, having no peak, acurve is shown to fall downward toward the right, and in the case of aspecimen of the compound composed of uniformly distributed titanium andsilicon (FIG. 14), the curve has a downward dent at points thereof,corresponding to the respective intensity ratios at the peaks oftitanium and silicon, respectively. In contrast, in the case of theforeign particle (titanium) on the wafer (FIG. 13), the curve has anupward bulge at a point thereof, corresponding to the intensity ratio atthe peak of titanium while the curve has a downward dent at a pointthereof, corresponding to the intensity ratio at the peak of silicon.Furthermore, the downward dent in FIG. 13 is shown to be a furtherdeeper dent in comparison with that in the case of the specimen of thecompound composed of uniformly distributed titanium and silicon. On thebasis of the above finding, there are displayed results of determinationthat titanium is the element of the foreign particle, and silicon is asubstance underneath the foreign particle.

[0096]FIG. 12 shows scattering conditions of electrons inside a specimenof a titanium thin film 50 nm thick, attached to the top of a siliconsubstrate, as calculated by a Monte Carlo method. FIG. 12A shows acalculation result in the case of electron beam irradiation at 3 kV ofacceleration voltage, and FIG. 12B shows a calculation result in thecase of electron beam irradiation at 5 kV of acceleration voltage. Aproportion of electrons penetrating through the titanium thin film to bescattered inside the silicon substrate in the case of the accelerationvoltage at 3 kV is higher that that in the case of the accelerationvoltage at 5 kV. Accordingly, X-rays produced by the electron beamirradiation at 3 kV of the acceleration voltage represent more X-raysemitted from substance in the vicinity of the surface, that is,titanium, than those emitted from the substrate, that is, silicon. Theabove-described results of the determination based on difference ingraph between FIGS. 13 and 14 are derived by taking advantage of such aphenomenon as described. That is, with the present embodiment, itbecomes possible to provide information concerning elementaldistribution from an intensity ratio between X-ray spectra as observed,so that a cause of generation of a foreign particle can be searched forwith greater accuracy.

[0097] With the present embodiment, there is shown the method ofidentifying elements of a foreign particle with X-ray spectra emitted byelectron beam irradiation at two varied acceleration voltages. Now,referring to FIGS. 16, and 17, there is described hereinafter anothermethod of identifying elements of a foreign particle by use of threevaried acceleration voltages. FIGS. 16A through 16C are schematicrepresentations for illustrating the principle on which this method isbased, and FIGS. 17A through 17C are schematic diagrams of X-rayspectra. As shown in FIGS. 16A through 16C, this method is effective notfor a process step as an object for inspection, but for analysis of aforeign particle called a foreign particle abnormal in shape, generateddue to a foreign particle 22 immediately before the process step. InFIGS. 16A through 16C, reference numeral 21 denotes a substrate after astep proceeding to the process step as the object for the inspection,and 26 denotes a film formed in the process step as the object for theinspection. FIG. 16C is a sectional view showing a portion abnormal inshape, generated due to the foreign particle 22 formed immediatelybefore the process step as the object for inspection. First, as show inFIG. 16A, the portion abnormal in shape is irradiated with an electronbeam 8 at an acceleration voltage selected so as not to pass through thefilm 26, whereupon the electron beam 8 scatters in an electronscattering region 71, and only a characteristic X-ray peak 72 of theelement of the film 26 is observed as shown in FIG. 17A. FIG. 16B showsa case of irradiation with an electron beam 8 having an accelerationvoltage higher than that for the electron beam 8 in FIG. 16A. With theacceleration voltage getting higher, the electron beam scatters insidethe foreign particle 22 as shown by an electron scattering region 71. Inthis case, as shown in FIG. 17B, besides the characteristic X-ray peakcorresponding to the element of the film 26, a characteristic X-ray peak73 corresponding to the element of the foreign particle 22 is observed.Next, as shown in FIG. 16C, an electron beam 8 having a still higheracceleration voltage is irradiated, whereupon the electron beam 8 comesto scatter inside the substrate 21 in the step proceeding to the processstep for the inspection, as indicated in the figure, so that acharacteristic X-ray peak 74 corresponding to the element of thesubstrate 21 is observed. Thus, with this method, it becomes possible toobtain information concerning the element of the foreign particle 22.

[0098] The invention has advantageous effects as follows. That is, withthe above-described embodiments of the invention, it becomes possible toobserve foreign particles on the surface of a specimen by electron beamirradiation on condition that X-ray spectra from the foreign particlescan be detected with high resolving power and high efficiency while highprecision matching with reference spectra can be implemented andeffective analysis can be performed even with a few reference spectraeven in case there occur problems at the time of X-ray analysis byexcitation with an electron beam at low acceleration voltages,considered effective for observation of elements of the foreignparticles as the objects of inspection with high space resolving power,that is, in the case where characteristic X-rays that can be excited arerestricted, peaks of the characteristic X-ray that can be excited areoverlapped with each other, and the X-ray spectra of the foreignparticles are mixed with the X-ray spectrum of a substrate underneaththe foreign particles. Furthermore, it is also possible to obtaininformation concerning distribution of observed elements inside thespecimen. Thus, elemental analysis with high precision and highsensitivity can be performed, and it becomes possible to provide anelectron microscope including an apparatus of x-ray analysis, capable ofperforming inspection of foreign particles for enhancement of yields inmanufacturing LSI device and so forth, attaining furtherminiaturization, with high precision, and high space resolving power,and a method of analyzing specimens using the same.

What is claimed is:
 1. An electron microscope having an electron beamoptical system provided with an electron source and a lens for focusingan electron beam, an optical system controller for controlling theelectron beam optical system, a specimen stage on which a specimen is tobe placed, an electron detector for detecting electrons emitted from thespecimen by irradiating the specimen with the electron beam, an X-raydetector for detecting X rays radiated from the specimen, and aprocessor for processing signals from both the detectors, and performingimage formation and elemental analysis of the specimens, said electronmicroscope comprising: a database having data including X-ray spectra(reference spectra) of a plurality of kinds of standard substances andlabels containing names of substances corresponding to the respectivereference spectra; and means comprising steps of: checking an X-rayspectrum (sample spectrum) of the specimen against the reference spectrain the database; calculating degree of matching in spectral shapebetween the sample spectrum and the reference spectra; extracting areference spectrum having the highest degree of matching from thedatabase; setting up a plurality of X-ray energy regions so as to havesensitivity data for X-ray energy of the X-ray detector, and to includepeaks of the sample spectrum when analyzing by identifying a substanceof the specimen on the basis of the label corresponding to the referencespectrum extracted; standardizing intensity of the reference spectrainto intensity of the sample spectrum for each of the X-ray energyregions as set up after multiplying the reference spectra by thesensitivity data; checking the sample spectrum against the referencespectra as standardized and extracting one or a plurality of thereference spectra in descending order of the degree of matching betweenthe sample spectrum and the reference spectra for each of the X-rayenergy regions; and outputting the label or labels corresponding to theone or the plurality of the reference spectra, degree of matching, and anumerical value used in the standardization.
 2. An electron microscopeaccording to claim 1, wherein a function of outputting the label, thedegree of matching, and the numerical value used in the standardizationoutputs a first candidate element, first to second candidate elements,or first to third candidate elements in descending order of the degreeof matching.
 3. An electron microscope according to claim 1, wherein aintensity ratio of the sample spectra obtained by electron beamirradiation at not less than two varied acceleration voltages isdisplayed.
 4. An electron microscope according to claim 1, wherein thesensitivity data contain a ratio of an intensity of an X-ray spectrum ofa standard specimen including a silicon wafer, obtained at the time ofobtaining the reference spectra to an intensity of an X-ray spectrum ofthe standard specimen, obtained immediately before matching.
 5. Anelectron microscope having an electron beam optical system provided withan electron source and a lens for focusing an electron beam, an opticalsystem controller for controlling the electron beam optical system, aspecimen stage on which a specimen is to be placed, an electron detectorfor detecting electrons emitted from the specimen by irradiating thespecimen with the electron beam, an X-ray detector for detecting X raysradiated from the specimen, and a processor for processing signals fromboth the detectors, and performing image formation and elementalanalysis of the specimens, said electron microscope comprising: adatabase having data including X-ray spectra (reference spectra) of aplurality of kinds of standard substances and labels containing names ofsubstances corresponding to the respective reference spectra; a memoryfor storing a plurality of X-ray spectra (sample spectra) at a pluralityof observation points on the specimen, respectively, obtained by theX-ray detector; and means of categorizing the plurality of the samplespectra into one or a plurality of groups of the sample spectra bymatching thereof with each other, and performing elemental analysis ofone X-ray spectrum selected from the respective groups.
 6. An electronmicroscope according to claim 5, further comprising a function ofmatching the sample spectra with each other for each of one or aplurality of X-ray energy regions set up so as to include respectivepeaks of the sample spectra when executing the matching of the samplespectra with each other.
 7. An electron microscope having an electronbeam optical system provided with an electron source and a lens forfocusing an electron beam, an optical system controller for controllingthe electron beam optical system, a specimen stage on which a specimenis to be placed, an electron detector for detecting electrons emittedfrom the specimen by irradiating the specimen with the electron beam, anX-ray detector for detecting X rays radiated from the specimen, and aprocessor for processing signals from both the detectors, and performingimage formation and elemental analysis of the specimens, said electronmicroscope comprising: means of detecting the count-number of X rays perunit time by detecting the X rays with the X-ray detector, andfeedback-controlling current quantity of the electron beam on the basisof the count-number of X rays per unit time.
 8. An electron microscopeaccording to claim 7, wherein the current quantity of the electron beamis feedback-controlled such that the count-number of X rays from thespecimens falls within a range of 1000 to 2000 counts per second.
 9. Amethod of analyzing specimens, using an electron microscope having anelectron beam optical system provided with an electron source and a lensfor focusing an electron beam, an optical system controller forcontrolling the electron beam optical system, a specimen stage on whicha specimen is to be placed, an electron detector for detecting electronsemitted from the specimen by irradiating the specimen with the electronbeam, an X-ray detector for detecting X rays radiated from the specimen,a processor for processing signals from both the detectors, andperforming image formation and elemental analysis of the specimens, anda database having data including X-ray spectra (reference spectra) of aplurality of kinds of standard substances and labels containing names ofsubstances corresponding to the respective reference spectra, saidmethod of analyzing the specimens comprising steps of: checking an X-rayspectrum (sample spectrum) of the specimen against the reference spectrain the database; calculating degree of matching in spectral shapebetween the sample spectrum and the reference spectra; extracting areference spectrum having the highest degree of matching from thedatabase; setting up a plurality of X-ray energy regions so as to havesensitivity data for X-ray energy of the X-ray detector, and to includepeaks of the sample spectrum when analyzing by identifying a substanceof the specimen on the basis of the label corresponding to the referencespectrum extracted; standardizing intensity of the reference spectrainto intensity of the sample spectrum for each of the X-ray energyregions as set up after multiplying the reference spectra by thesensitivity data; checking the sample spectrum against the referencespectra as standardized and extracting one or a plurality of thereference spectra in descending order of the degree of matching betweenthe sample spectrum and the reference spectra for each of the X-rayenergy regions; and outputting the label or labels corresponding to theone or the plurality of the reference spectra, the degree of matching,and a numerical value used in the standardization.
 10. A method ofanalyzing specimens, using an electron microscope having an electronbeam optical system provided with an electron source and a lens forfocusing an electron beam, an optical system controller for controllingthe electron beam optical system, a specimen stage on which specimensare to be placed, an electron detector for detecting electrons emittedfrom the specimens by irradiating the specimens with the electron beam,an X-ray detector for detecting X rays radiated from the specimens, aprocessor for processing signals from both the detectors, and performingimage formation and elemental analysis of the specimens, a databasehaving data including X-ray spectra (reference spectra) of a pluralityof kinds of standard substances and labels containing names ofsubstances corresponding to the respective reference spectra, and amemory for storing a plurality of X-ray spectra (sample spectra) at aplurality of observation points on the specimens, respectively, obtainedby the X-ray detector, said method of analyzing the specimenscomprising: means of categorizing the plurality of the sample spectrainto one or a plurality of groups of the sample spectra by matchingthereof with each other, and performing elemental analysis of one X-rayspectrum selected from the respective groups.